The study, published in the Journal of the American Medical Association, looked at about 1,800 children in grade one from 12 primary schools in Guangzhou, China.

　　About half of the students were assigned to one additional 40-minute class of outdoor activities, which was added to each school day, and their parents were encouraged to engage their children in outdoor activities after school hours, especially during weekends and holidays.

　　The other half children and their parents continued their usual pattern of activity.

　　More time outdoors may cut kids risk of nearsightedness: <a href=http://www.hxen.com target=_blank class=infotextkey>study</a>

　　At the end of the three-year study, 30.4 percent of children who spent more time outdoors were nearsighted, compared to 39.5 percent of those in the control group.

　　"Our study provided the highest level of evidence for myopia prevention and control that outdoor activities, as a simple public health intervention, may significantly reduce the rate of myopia without affecting the schoolwork," lead author He Mingguang, professor of Sun Yat-sen University, told Xinhua.

　　He said an addition of two-hour daily outdoor activities may help achieve the goal of controlling the occurrence of myopia, commonly known as nearsightedness.

　　The researchers called the results "clinically important" because small children who develop myopia early are most likely to progress to high myopia.

　　"Thus a delay in the onset of myopia in young children, who tend to have a higher rate of progression, could provide disproportionate long-term eye health benefits," they wrote in the paper.

　　In an accompanying editorial, Michael Repka of the Johns Hopkins University School of Medicine said establishing the long-term effect of additional outdoor activities on the development and progression of myopia is "particularly important" because the intervention is "essentially free and may have other health benefits."